Virtual Colossus

Bringing the world's first electronic digital computer into the 21st Century

Virtual Colossus 3D
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What was Colossus and why a virtual one?

Colossus was the name of a series of computers developed by British codebreakers in 1943-1945 to help in the cryptanalysis of the Lorenz cipher. After the war, the Colossus computers were destroyed and all plans and information was required to be incinerated.

In 1992, Tony Sale and his team began the ambitious task of rebuilding a working Colossus from scraps of information and a few photos - they succeeded and you can see this running for real at The National Museum of Computing in Bletchley Park.

Tony Sale also wrote a virtual version of this amazing machine in 2001, but it's tricky to get running as it was written for a very old version of Internet Explorer.
See if you want to give it a go.

To honour his memory and to make sure this code and it's story was not lost, in 2016, I rewrote a new Virtual Colossus using current browsers based on his original logic engine code and now, in 2020, a full 3D version you can walk around. My hope is that more people will get to know this incredible story about the first computer.

What do I need to know to run it!
Instructions for use


You'll need a recent PC/Mac with a 3d capable graphics card with an up-to-date internet browser1 or a fast tablet/phone2.
If you're finding it too slow or movement jumpy, try switching off the options marked "Show Rear Valves" and/or "Show Front Valves" on the control panel.

1For Internet Browser, we recommend Google Chrome on both PC and Mac.
2To enable the touch screen movement controls, press Restart in Touch Mode on the control panel.

Switching between View/Cursor modes

Using the default Mouse/Keyboard control, there are two modes, one where a cursor is available to change switches and dials and the other to look around.

Click on the screen anywhere the standard cursor arrow is shown to move into View mode and click again to move back to Cursor mode.

View mode

View mode allows you to use the mouse to look around, while in this mode, the cursor will be hidden.

Use the keys WASD to move forward, left, right and backwards.

Click anywhere to switch to Cursor mode so you can change switches.

Cursor mode

Cursor mode allows you to interact with the switches, dials and plugs on Virtual Colossus.

Move the cursor over a switch until you see the hand cursor then click and drag in the directions specified.

Change back to view mode by clicking whenever you see the arrow cursor.

Look for Info Boxes

Look for the helpful blue info boxes and click on them to open up a help screen.

These give extra information about panels and racks and will help you to learn how to interact with the switches and dials.


Download a tutorial on using Virtual Colossus to break a Lorenz message.
You can also follow this at any time by using the button "How to decrypt a Lorenz message" on the main simulation.

Get Tutorial

Running on a phone or tablet

If you're on a fast phone or tablet, switch to touch screen mode by pressing on "Restart in Touch Mode" once on the main simulation. Switch off Rear & Front valve rendering to make it a little faster. If not, maybe try our original 2D version.

Run Virtual Colossus 2D

View Scenarios to run yourself

A series of intercept scenarios and challenges for you to run on Colossus!


The National Museum of Computing

The National Museum of Computing, located on Bletchley Park, is an independent charity housing the world's largest collection of functional historic computers, including the rebuilt Colossus, the world’s first electronic computer, and the WITCH, the world's oldest working digital computer. The museum enables visitors to follow the development of computing from the ultra-secret pioneering efforts of the 1940s through the large systems and mainframes of the 1950s, 60s and 70s, and the rise of personal computing in the 1980s and beyond.

The museum does not receive government or Lottery funding - their work in keeping the history of computing alive is really important and the teams of volunteers restoring and keeping these machines working are so dedicated!

Virtual Colossus 3D (and all my other simulations) are free for you to use, but if you enjoyed learning about running Colossus, and are able, could I suggest making a donation, buying something from their online shop or even becoming a supporter or sponsor to enable them to continue teaching future generations.

Tony and Margaret Sale and the rebuild team .. without their foresight and hard work, the full details of this marvelous machine could have been lost forever and we certainly would not have been able to see it actually running! Margaret worked tirelessly to make TNMOC the amazing place that it is today.

Tony's original website is still available here and contains a lot of information including his original Virtual Colossus software. .. Bletchley Park is an incredible site with an amazing story to tell and is so worth a visit (or two, or three). I'm still finding out new things about the work of the incredible men & women who served here during the war each time I visit.

The engineers behind Colossus

Tommy Flowers .. A true genius and way ahead of his time, Allen Coombs, Dr Arnold Lynch and all the engineers at Dollis Hill

The geniuses at Bletchley Park

Brigadier John Tiltman .. A giant among cryptanalysts

The Bill Tutte Memorial Fund .. "Bill Tutte achieved one of the greatest intellectual feats of World War Two by breaking the extremely complex Lorenz code without ever seeing the machine that generated it."

Captain Jerry Roberts and all the codebreakers in the Testery. Without these people's code breaking skills and their daily breaking of the Lorenz wheels, Colossus would have been unable to function.

Plus all the other people who worked hard at Bletchley Park including all the Wrens(WRNS) who were the first computer operators in the world!

3D software

A couple of amazing (and free to use) tools which enabled me to write Virtual Colossus 3D

three.js is a cross-browser JavaScript library for creating 3D computer graphics in a web browser and an amazing piece of work. A big thank you to Mr.Doob for creating this wonder! a free and open source 3D creation suite which was used to create the models.

Let me know what you think!

Have I got something wrong, it doesn't work quite correctly on your computer or maybe you just want to say hi - check my Facebook or Twitter pages

Martin Gillow